nebula  astronomy: a gas-mass or dust-mass within a galaxy. figurative:
something ill-defined or insubstantial; a hazy mass or cloud.

necromancy(also here, hereand here)  1.
witchcraft or black magic 2. predicting the future by communicating with
the dead [Note: dictionary at mancy lists 54 form of divination]
Interesting etymology: from Greek necro = "dead". When the Latin word came to mean
"black arts", the spelling changed to nigromantia
(Latin niger "black,"), and
came into Middle English with the nigro-"black" root. Modern
spelling is from attempts to correct this back to the original "dead"
meaning.

neologism  a newly coined
word or expression;
the act of so coining. (Also applies to coining new phrases or meanings)

neophobia  fear or dislike of
anything new or unfamiliar [often used for a childs refusal to try a new food,
particularly vegetables!]

neophyte  (also here)  a person who is new
to a subject or activity; a beginner, a novice (also, a novice in a
religious order, or a newly ordained priest)

neoteny  the retention of
juvenile features in an adult animal (or sometimes used to mean: the
characteristic of having a relatively long period of development)

neoteric 
(of an author or other person): of recent times; modern; also, having a
modern outlook
(of beliefs, practices, or other things): modern, recent, new
Also used as a noun. Not necessarily
complimentary; Freq. with disparaging connotations, says OED;
objectionably novel, newfangled.

nepenthe  1. a drug mentioned in the Odyssey as
a remedy for grief; hence 2. something that induces forgetfulness of
sorrow or eases pain.

nestcock  obs. a househusband; a man who stays at home and manages the
house while his wife goes to work

nestor;Nestor  eponym: a venerable and wise
old man; a patriarch in a field

nettle  to goad or provoke, as by constant criticism; also, to
annoy, disturb, esp. by minor irritations

neurasthenia  a psychological
disorder characterized by chronic fatigue and weakness with vague physical
symptoms (headache, muscle pain, etc.); originally attributed to weakness or
exhaustion of the nerves. Now considered an outdated diagnosis  but is it
anything other than what we now call chronic fatigue syndrome?

niding  a coward; a dastard; a term of
utmost opprobrium. (also written nithing)

niggardly  grudging and petty; meanly small: left the waiter a niggardly tip.
(Though this word has nothing to do with the so-called "N-word," one
does well to avoid it due to the ignorance of many readers or listeners.)

nihilism  (also nihilist; nihilistic) 1. doctrine that social
institutions are so bad that destruction is desirable for its own sake,
independent of any constructive program 2. rejection of all moral
or religious values

nikkei  see issei

nimgimmer  a physician or surgeon, particularly those who cure venereal
disease

ninety-nine  used by physicians to detect
areas of the lungs that have become solidified, as from pneumonia. When the
patient speaks or whispers, the sound is loudest in these areas, and the
loudness can be noticed by stethoscope or by a palm on the patients back.

ningimmer  a physician or surgeon, particularly those who cure the
venereal disease

niveous  resembling snow; snowy; also,
snow-white. (Note: There's an odd schism in how the lexicographers handle
this word. AHD gives "resembling snow; snowy", but omits the
specific definition as "white". Most on-line dictionaries are similar
but the thesauri  even the one at AHD's site  consistently list niveous as a synonym for
"white". )

opposition  c.1395, as an astrological term
for two heavenly bodies exactly across from one another in the sky. The meaning
"contrast, antagonism" first attested 1581; sense of "political
party opposed to the one in power" is from 1704.

pac man defense a stratagem, to prevent a hostile
takeover, by which the target company tries to acquire the bidder

pace (Latin)  with due deference to; used to acknowledge politely
someone with whom the writer disagrees

pagan (etymology)  from Latin for
villager, rustic. Tied to "nature worship" because
conservative villagers clung to the old nature gods after the Christianization
of Roman towns and cities. (alternate reason for that tie: 'villager' was Roman
military-slang for an incompetent soldier, and the early church, with its
military image, picked up this concept for "those outside the Church
Militant".)

palimpsest  a manuscript on which more than one text has been written atop an
earlier one which, incompletely erased, is visible; also, an object or a
place whose older layers or aspects are apparent beneath its surface

parhelion  a bright spot in
the sky, often in pairs on either side of the sun, thus forming a "triple
sun". Caused by atmospheric ice crystals. (A parhelion is also
called a sun-dog. The same phenomenon with the
moon is called a paraselene or moon
dog.)

parishion  parishioner; a member of a parish. This word died out in the 16th
century, but it is an answer to the quiz, "Name 3 words ending in  shion:
cushion, fashion, and ____." See also hushion, fushion.

Park Avenue  the world of those who are
ultra-rich in both money and social standing

Parkinson's Law  eponym: the principle, Work expands so as
to fill the time available for its completion.

Parnassus  1. the world of poetry or
poets: a rhymester striving to enter Parnassus2. a center of poetry or artistic activity 3. a collection of
poems

parody  a literary
composition imitating (and esp. one satirizing) another work. Also,
by extension: a poor or feeble imitation; a travesty

paronomasia  punning. more specifically, the
form of pun based on using two different words of same or similar sound.
(contrast antanaclasis, syllepsis, zeugma)

parricide  the killing of [or
the killer of] ones own parent  usually the father  or other near relative

patronymic  adj. and noun: of a name derived from
one's father or paternal ancestor

pavilion  (originally, a butterfly) a
large and ornate tent. But more commonly applied structures of greater
permanence, as a light roofed structure (picnic pavilion), a solid but
temporary structure (a pavilion at the World's Fair), a sports/entertainment
arena, or a building within a complex (as a hospital).

pavlovian  eponym: being or expressing a conditioned or predictable
reaction; automatic

pavonine  with the iridescence of a
peacock's tail. (also, "peacock-like", in the manner of such
words as canine, feline, etc.)

pawl [pronounced like pall]
 a hinged
bar whose free end engages the teeth of a ratchet wheel, allowing it to
turn in one direction only

pawn  a person without real power,
used (manipulated) by others for their own purposes [term evolved from the game
of chess]

pentimento a visible trace of the artists
earlier version, showing through when the upper layers of the paint have become
translucent with age. (In effect, the painting behind the painting, showing
where the artist changed his mind and changed his work.)

penumbra1.a partial shadow (blocked from some but not all light sources and their
parts) between regions of complete shadow and complete illumination2.figurative
extension:a.an adjoining region in which something
shades off into lessened intensely [thepenumbraof the downtown]b.something that partially covers, surrounds,
or obscures

peony shell  fireworks: a spherical burst firework,
in which the stars do not leave a trail

perseity  medieval philosophy: the quality of having substance
independently of any real object

persiflage  friendly banter or frivolous
conversation (persifleur  one who indulges in
persiflage; a banterer)[From
French, but there it means to mock, to ridicule. The root is siffler, to
hiss, akin to sibilant.]

Peter Principle  eponym; coinage: the principle that
those in a hierarchy are promoted until they reach the level at which they are
no longer competent (at which point promotion ceases). Thus each position is
eventually filled by an incompetent.